/*
 * Created on Feb 5, 2008
 * Created by Olivier Chalouhi
 * 
 * Copyright (C) Azureus Software, Inc, All Rights Reserved.
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License only.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */

package com.aelitis.azureus.core.util.png;

import java.nio.ByteBuffer;
import java.security.InvalidParameterException;

public abstract class CRCedChunk extends Chunk {

    private byte[] type;

    public CRCedChunk(byte[] type) throws InvalidParameterException {
        if (type.length != 4) {
            throw new InvalidParameterException("type must be of length 4, provided : " + type.length);
        }
        this.type = type;
    }

    public byte[] getChunkPayload() {

        byte[] contentPayload = getContentPayload();
        int length = contentPayload.length;
        ByteBuffer buffer = ByteBuffer.allocate(length + 12);
        buffer.putInt(length);
        buffer.put(type);
        buffer.put(contentPayload);

        buffer.position(4);
        buffer.limit(length + 8);

        long crc = crc(buffer);
        buffer.limit(length + 12);
        buffer.putInt((int) crc);

        buffer.position(0);
        return buffer.array();

    }

    public abstract byte[] getContentPayload();

    /* Table of CRCs of all 8-bit messages. */
    private static long[] crc_table = new long[256];

    /* Flag: has the table been computed? Initially false. */
    private static boolean crc_table_computed = false;

    /* Make the table for a fast CRC. */
    private static synchronized void make_crc_table() {
        long c;
        int n, k;

        for (n = 0; n < 256; n++) {
            c = (long) n;
            for (k = 0; k < 8; k++) {
                if ((c & 1) != 0)
                    c = 0x0edb88320L ^ ((c >> 1) & 0x0FFFFFFFF);
                else
                    c = c >> 1;

                c = c & 0x0FFFFFFFF;
            }
            crc_table[n] = c;
        }
        crc_table_computed = true;
    }

    /*
     * Update a running CRC with the bytes buf[0..len-1]--the CRC should be initialized to all 1's, and the transmitted value is the 1's complement of
     * the final running CRC (see the crc() routine below).
     */

    private static long update_crc(long crc, ByteBuffer buf) {
        long c = crc;

        if (!crc_table_computed) {
            make_crc_table();
        }
        while (buf.hasRemaining()) {
            c = crc_table[(int) ((c ^ buf.get()) & 0xff)] ^ (c >> 8);
        }
        return c;
    }

    /* Return the CRC of the bytes buf[0..len-1]. */
    private static long crc(ByteBuffer buf) {
        return update_crc(0xffffffffL, buf) ^ 0xffffffffL;
    }

}
